Positive and Negative Ions: Cations and Anions

Cations (positively-charged ions) and anions (negatively-charged ions) are formed when a metal loses electrons, and a nonmetal gains those electrons. The electrostatic attraction between the positives and negatives brings the particles together and creates an ionic compound, such as sodium chloride.

A metal reacts with a nonmetal to form an ionic bond. You can often determine the charge an ion normally has by the element’s position on the periodic table:

  • The alkali metals (the IA elements) lose a single electron to form a cation with a 1+ charge.

  • The alkaline earth metals (IIA elements) lose two electrons to form a 2+ cation.

  • Aluminum, a member of the IIIA family, loses three electrons to form a 3+ cation.

  • The halogens (VIIA elements) all have seven valence electrons. All the halogens gain a single electron to fill their valence energy level. And all of them form an anion with a single negative charge.

  • The VIA elements gain two electrons to form anions with a 2- charge.

  • The VA elements gain three electrons to form anions with a 3- charge.

The first table hows the family, element, and ion name for some common monoatomic (one atom) cations. The second table gives the same information for some common monoatomic anions.

Some Common Monoatomic Cations
Family Element Ion Name
IA Lithium Lithium cation
Sodium Sodium cation
Potassium Potassium cation
IIA Beryllium Beryllium cation
Magnesium Magnesium cation
Calcium Calcium cation
Strontium Strontium cation
Barium Barium cation
IB Silver Silver cation
IIB Zinc Zinc cation
IIIA Aluminum Aluminum cation
Some Common Monoatomic Anions
Family Element Ion Name
VA Nitrogen Nitride anion
Phosphorus Phosphide anion
VIA Oxygen Oxide anion
Sulfur Sulfide anion
VIIA Fluorine Fluoride anion
Chlorine Chloride anion
Bromine Bromide anion
Iodine Iodide anion

It’s more difficult to determine the number of electrons that members of the transition metals (the B families) lose. In fact, many of these elements lose a varying number of electrons so that they form two or more cations with different charges.

The electrical charge that an atom achieves is sometimes called its oxidation state. Many of the transition metal ions have varying oxidation states. The next table shows some common transition metals that have more than one oxidation state.

Some Common Metals with More than One Oxidation State
Family Element Ion Name
VIB Chromium Chromium(II) or chromous
Chromium(III) or chromic
VIIB Manganese Manganese(II) or manganous
Manganese(III) or manganic
VIIIB Iron Iron(II) or ferrous
Iron(III) or ferric
Cobalt Cobalt(II) or cobaltous
Cobalt(III) or cobaltic
IB Copper Copper(I) or cuprous
Copper(II) or cupric
IIB Mercury Mercury(I) or mercurous
Mercury(II) or mercuric
IVA Tin Tin(II) or stannous
Tin(IV) or stannic
Lead Lead(II) or plumbous
Lead(IV) or plumbic

Notice that these cations can have more than one name. The current way of naming ions is to use the metal name, such as Chromium, followed in parentheses by the ionic charge written as a Roman numeral, such as (II).

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